Identification of type VI secretion system effector-immunity pairs using structural bioinformatics

Alexander M. Geller, Maor Shalom, David Zlotkin, Noam Blum, Asaf Levy*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The type VI secretion system (T6SS) is an important mediator of microbe–microbe and microbe–host interactions. Gram-negative bacteria use the T6SS to inject T6SS effectors (T6Es), which are usually proteins with toxic activity, into neighboring cells. Antibacterial effectors have cognate immunity proteins that neutralize self-intoxication. Here, we applied novel structural bioinformatic tools to perform systematic discovery and functional annotation of T6Es and their cognate immunity proteins from a dataset of 17,920 T6SS-encoding bacterial genomes. Using structural clustering, we identified 517 putative T6E families, outperforming sequence-based clustering. We developed a logistic regression model to reliably quantify protein–protein interaction of new T6E-immunity pairs, yielding candidate immunity proteins for 231 out of the 517 T6E families. We used sensitive structure-based annotation which yielded functional annotations for 51% of the T6E families, again outperforming sequence-based annotation. Next, we validated four novel T6E-immunity pairs using basic experiments in E. coli. In particular, we showed that the Pfam domain DUF3289 is a homolog of Colicin M and that DUF943 acts as its cognate immunity protein. Furthermore, we discovered a novel T6E that is a structural homolog of SleB, a lytic transglycosylase, and identified a specific glutamate that acts as its putative catalytic residue. Overall, this study applies novel structural bioinformatic tools to T6E-immunity pair discovery, and provides an extensive database of annotated T6E-immunity pairs.

Original languageAmerican English
JournalMolecular Systems Biology
StateAccepted/In press - 2024

Bibliographical note

Publisher Copyright:
© The Author(s) 2024.


  • Alphafold-multimer
  • Effector-immunity Pairs
  • Foldseek
  • Structural Bioinformatics
  • Type VI Secretion System (T6SS)


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